From the Vibram site:
The typical human foot is an anatomical marvel of evolution with 26 bones, 33 joints and more than 100 muscles, tendons and ligaments. Like the rest of the body, to keep our feet healthy, they need to be stimulated and exercised.
Thatâ€™s why we recommend wearing FiveFingers for exercise, play, and for fun. Stimulating the muscles in your feet and lower legs will not only make you stronger and healthier, it improves your balance, agility and proprioception.